There exists a number of requirements for a means to respond quickly to the presence of certain classes of liquids, for example salt water. For example, it is necessary to separate an aviator from his parachute canopy very quickly as soon as he is immersed in salt water, but also there exists the need for insensitivity to pure water or to saline solutions of lesser concentration than that of ocean water in order that the canopy will not be released when falling through a rain storm or approaching the surface or turbulent water where the spray would be diluted saline, because then the aviator would be separated from his chute while still in the air.
Numerous sensors, generally electronic or current-conduction types, have been suggested for this application, but often they are too sensitive or too insensitive, too complicated, employ excessive force for the separation, or involve a combination of two or more of these problems.
Other useful examples are such as sensing external concentrations, relative to a standard concentration.
It is an object of this invention to provide a sensor which is responsive to external solute concentrations by providing an osmotic effect, which can quickly and reliably provide a signal, and if desired, also an actuating means in response to the external presence of some species, such as an ionic species.
Also, it is an object of this invention to provide such a sensor which is passive, and whose response is in no way dangerous to a person carrying it.